In general, SIR systems perform a number of functions including crash sensing, diagnostics, signal processing and analysis, and deployment of one or more restraint devices such as frontal or side air bags or seat belt pretensioners. When the system is designed such that the components for performing most or all of these functions are packaged together in a single electronic module, the system architecture may be characterized as centralized. When the system is designed so that the components are separately packaged based on functionality and interconnected by a communications bus, the system architecture may be characterized as distributed.
The selection of centralized vs. distributed architecture depends upon a number of factors, including the number of restraint devices, controller throughput requirements, package size, system cost and assembly considerations. In relatively simple mechanizations involving a small number of restraint devices and limited sensing and processing requirements, the centralized architecture may offer cost and assembly advantages. In relatively complex mechanizations involving a large number of restraint devices and sophisticated sensing and processing requirements, the distributed architecture may offer packaging and processing advantages.
A system architecture of the centralized type is schematically represented by the block diagram of FIG. 1. Referring to FIG. 1, the centralized system comprises a high function central processor and a number of side impact sensors, occupant sensors and restraint initiator modules. The central processor includes frontal acceleration sensor(s), power supply and energy reserve devices, interface circuitry for communicating with the sensor and initiator modules, a microprocessor for processing the sensor signals and executing the deployment algorithm, diagnostic circuitry and firing circuits for each of the restraint initiators. The remote side impact sensors provide information which may be difficult to sense in a central location of the vehicle, and the remote occupant sensors provide information about occupant position that is taken into consideration by the deployment algorithm.
A system architecture of the distributed type is schematically represented by the block diagram of FIG. 2. Referring to FIG. 2, the distributed system still includes a central processor, but the sensors and initiator driver circuits are located remote from the central processor, and communicate with the central processor via the communications bus. The role of the central processor as a communications interface now becomes more important, and other functions such as deployment control may be performed in the remote modules, enabling the functionality of the central processor to be minimized, or even up-integrated into another multi-function controller. Additionally, the flexibility of the system is increased since adding further sensors and/or initiators has only a modest impact on system cost.
Despite the many advantages of the distributed SIR system architecture, a potential disadvantage concerns the tolerance of the system to wiring faults in the communications bus, such as shorts to battery, shorts to ground, open circuits and shorts across the bus wires.